The existence of soil exchangeable Al in toxic levels inhibits root growth and elongation, with negative effects on water and nutrient uptake, especially of P. Thus, as soil P increases, plants become less dependent on a large root system, that may decrease crop response to liming. This study was carried out to evaluate the effect of liming and phosphorus fertilization on corn yield. The experiment was conducted in Lages, Southern Brazil, from 1994 to 1998, in a clayed Oxisol (Hapludox) with pH 4.7, exchangeable Al of 39 mmol c kg-1, P of 1.0 mg kg-1, and liming requirement of 9 t ha-1 to raise soil water pH to 6.0. Treatments consisted of a factorial with three rates of liming (0, 4.5 and 9.0 t ha-1) and four of P2O5, respectively 60, 120, 180 and 240 kg ha-1 in the first crop; 40, 80, 120 and 160 kg ha-1 in the second and fourth crop; and 30, 60, 90, and 120 kg ha-1 in the third crop. The effect of liming increased with time from null in the first year up to increments of 39% on corn yield. On most growing seasons, yield increased up to pH 5.4, where half of the liming required to achieve pH 6.0 was applied. On treatments that received the two highest rates of P2O5 (127 and 170 kg-1 ha-1 per crop), liming had no effect on corn yield. Addition of P increased corn yield in all seasons but the magnitude decreased as soil pH increased. The highest productivities were obtained with recommended P rate in two growing seasons, but in the remaining two, it was necessary to apply 50% more.
liming; phosphorus fertilization; acid soils